Examiners Report June GCE Biology B 8BI0 02

Transcription

1 Examiners Report June 2016 GCE Biology B 8BI0 02

2 Edexcel and BTEC Qualifications Edexcel and BTEC qualifications come from Pearson, the UK s largest awarding body. We provide a wide range of qualifications including academic, vocational, occupational and specific programmes for employers. For further information visit our qualifications websites at or Alternatively, you can get in touch with us using the details on our contact us page at Giving you insight to inform next steps ResultsPlus is Pearson s free online service giving instant and detailed analysis of your students exam results. See students scores for every exam question. Understand how your students performance compares with class and national averages. Identify potential topics, skills and types of question where students may need to develop their learning further. For more information on ResultsPlus, or to log in, visit Your exams officer will be able to set up your ResultsPlus account in minutes via Edexcel Online. Pearson: helping people progress, everywhere Pearson aspires to be the world s leading learning company. Our aim is to help everyone progress in their lives through education. We believe in every kind of learning, for all kinds of people, wherever they are in the world. We ve been involved in education for over 150 years, and by working across 70 countries, in 100 languages, we have built an international reputation for our commitment to high standards and raising achievement through innovation in education. Find out more about how we can help you and your students at: June 2016 Publications Code 8BI0_02_1606_ER All the material in this publication is copyright Pearson Education Ltd GCE Biology B 8BI0 02

3 Introduction This was the first AS paper 2 examination of the new linear specification. There was a wide range in quality of answers with many excellent, well thought through and detailed answers. The new styles of AS papers place more emphasis on data analysis and interpretation, more questions in a practical context, an increased mathematical content and less scaffolding (resulting in fewer one or two mark questions). There are generally fewer mark points available for each question so that it is no longer possible to gain full marks for a question without giving a direct, correct answer. Many candidates demonstrated that they were able to interpret data and use their knowledge of the specification to draw appropriate conclusions. Calculations were generally carried out well, although very few candidates made reference to standard deviations in question 5(a) and many struggled to use percentages in question 7(b)(ii). Most candidates showed good factual knowledge of areas of the specification such as speciation and blood clotting but some found applying their knowledge to situations that they had not encountered previously difficult. Candidates who scored well were confident in the use of key scientific vocabulary and wrote answers that were often precise and well structured. There is a tendency for some candidates to think that they need to fill every line in an answer, a better guide to how much detail is required is the number of marks allocated to a question. A brief, carefully constructed answer, using key scientific vocabulary, is often more desirable than a poorly organised verbose one. GCE Biology B 8BI0 02 3

4 Question 1 (a) The majority of candidates gained both marks. Most correctly stated that active transport is the movement of substances against a concentration gradient and requires energy. A few confused active transport with diffusion or stated that it could operate both up and down a gradient. Examiner Comments This is a well structured answer that gains both mark points and clearly states the direction of the transport and the need for energy. Examiner Tip The number of marks allocated to a question should help you to structure your answer. This candidate clearly gets both mark points: movement against a gradient and the need for energy without using all the allocated lines. 4 GCE Biology B 8BI0 02

5 Question 1 (b) Many candidates found this question demanding although there were several excellent answers. Most understood that there would be an accumulation of chloride ions outside the cells (or in the intestine) but fewer went on to explain how this would lead to water loss by osmosis due to a lowering of water potential outside the cell. Many candidates referred to concentrations of water rather than water potential. At AS and A level, it is expected that candidates should refer to water potential rather than concentration. Question 1 (c) The majority of candidates were able to gain one mark on this question for the idea of a reduced diffusion of oxygen into the blood through the alveoli. Fewer appreciated that the mucus would block the airways leading to a reduced diffusion gradient. Although a knowledge of cystic fibrosis is not required for the specification, all the information needed to answer the question was given to the candidates. Some candidates failed to score due to poor quality of language, an example of a low quality answer would be: "less oxygen enters the lungs". This could easily be improved to: "less air carrying oxygen is able to be drawn through the bronchi into the alveoli". Question 1 (d) Many candidates were able to correctly recognise that the mutated allele leads to less water loss, but only more able candidates went on to explain how this would be an advantage in surviving cholera and enabling people to pass on this allele to their offspring. Some candidates tended to confuse the terms gene and allele and some do not quite understand the distinction between the command words describe and explain, often simply describing the data. GCE Biology B 8BI0 02 5

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7 Examiner Comments This answer explains how the allele reduces water loss and then points out that it is passed on to future generations. It almost gains a third mark point for the idea of survival but did not put this into the context of the question and imply that people were surviving cholera or the infection. Examiner Tip Always include the context of the question in your answers. It is not possible to gain full marks by giving a generic answer without relating it to the question. GCE Biology B 8BI0 02 7

8 Question 2 (a) (i) Many candidates gained both marks, although this seemed to depend upon whether candidates had experienced using photometers. Some candidates gave vague answers such as "allowing the experiment to work" and others seemed unaware that air bubbles would break the transpiration stream. Examiner Comments This answer gains one mark for the idea of preventing air bubbles entering the stem. The second mark is for an idea of the air bubbles breaking the water column; this answer gives an explanation that is too vague. Examiner Tip Give full details rather than vague answers. If it will "stop an experiment working" explain exactly why this is so. Examiner Comments This answer gains both marks. The candidate has explained that it is important to prevent air bubbles entering the stem and then explained how this would affect the experiment. 8 GCE Biology B 8BI0 02

9 Question 2 (c) This question generated a very good range of answers and many excellent explanations were seen that gained five or six marks. Each AS paper will carry one six mark question that is marked by using a level based mark scheme. The level based mark scheme has indicative content rather than defined statements. Candidates that gained high marks gave thorough descriptions of how transpiration rate and xylem diameter changed, linked this to changes in abiotic factors such as light intensity, explained how the changes would alter transpiration and linked this to cohesion - tension theory. Less able answers tended to simply describe the patterns with a limited explanation in terms of how abiotic factors would change and affect the rate of transpiration. Many candidates understood the cohesion - tension theory but only more able ones referred to details such as the hydrogen bonding of water molecules. Most were able to suggest one or two abiotic factors such as light intensity or wind speed but fewer actually gave a detailed explanation in terms of stomatal opening and diffusion gradients. There is a tendency for some candidates to revert to the security of GCSE knowledge when encountering an extended answer question. GCE Biology B 8BI0 02 9

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11 Examiner Comments This is a good level 2 answer. The candidate gives the basic pattern of transpiration and links this to environmental changes and cohesion tension. There is only a limited explanation of why transpiration rate changes and they have not correctly stated that the xylem diameter reduces at mid-day. GCE Biology B 8BI

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13 Examiner Comments This is a level 3 answer. There is a full explanation of how abiotic factors cause the changes in transpiration rate through the day and this is linked to the cohesion tension theory. It would require more depth in terms of the physiology behind the changes to gain six marks. GCE Biology B 8BI

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15 Examiner Comments This is a very strong, level 3 answer that gives very thorough and accurate explanations of the changes in transpiration and links them to the cohesion tension theory. It would be six marks but the candidate has mistaken a decrease in xylem diameter for an increase and so has not quite interpreted the data correctly. GCE Biology B 8BI

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17 Examiner Comments This is a level 2 answer. There is a limited explanation of the changes in transpiration rate linked to abiotic factors and an attempt at linking this to cohesion - tension theory. There is no explanation as to why abiotic factors would affect the rate and only basic consideration of what abiotic factors would cause changes. GCE Biology B 8BI

18 Question 3 (a) (i) The majority of candidates were able to gain at least one mark with many gaining both. This question tested candidates' ability to use the diversity index. Some less able candidates did not understand the meaning of the Σ (sum of) symbol. Examiner Comments This answer gains both marks and is an example of a correct calculation. Examiner Tip Always show all your working - you may get marks even if you don't get the correct final answer. 18 GCE Biology B 8BI0 02

19 Question 3 (a) (ii) The majority of candidates were able to gain at least one mark with many gaining two or three. Most were able to describe the increased number of butterfly species found on the organic field and many then went on to give an explanation of how chemicals such as herbicides and insecticides would affect the number of species. Surprisingly, only about half of the candidates made reference to the number of plant species and how this would affect the butterfly species. Candidates should try to include biological terms such as niche and habitat where appropriate. Question 3 (a) (iii) Most candidates were able to gain at least one mark on this question, with many going on to gain three or four. The majority recognised that abiotic factors, such as temperature, were not well controlled, and that the method of collection was not standardised. Typical examples of criticisms of the method included: not all butterflies being collected, the size of the sweep net and the method of sweeping. Fewer candidates recognised the lack of control of time and the need for more repeats to generate valid data. Now that there is no discrete "practical skills paper", candidates need to expect to be tested on experimental technique from both core and unfamiliar practicals. Examiner Comments This answer correctly criticises the experiment on the basis of the sweeping method, the abiotic factors not being controlled and the lack of repeats. GCE Biology B 8BI

20 Examiner Comments This answer gains three marks for: an understanding that the method is not standardised an understanding that factors such as temperature change an understanding that the time of year could affect the result. 20 GCE Biology B 8BI0 02

21 Question 3 (b) (i) Most candidates were able to correctly describe the changes in butterfly species number over the years although many did not notice the fact that the number levelled off or decreased in the final years. About half of candidates went on to correctly link the increased number of butterfly species with the increased number of plant species. Disappointingly, however, only a minority then explained this in terms of increased diversity of food. It is important to use precise language, and candidates should appreciate that "more food" is a different answer to "more variety of food sources". Examiner Comments This answer gained all three marks. The idea of an increase and a decrease in numbers of butterfly species is clear and this is linked to an increase in plant species. The candidate then points out that the butterflies feed on nectar; by itself this would not gain a mark, but as they have already explained that there are more plant species, the answer implies that there is more variety of food. Examiner Tip Although no credit was awarded for it in this question, this candidate carries out a calculation to support their answer - this is "good practice". GCE Biology B 8BI

22 Examiner Comments This answer gained two marks. There is a correct description of the change in butterfly species but no link to the increase in number of different plant species. The second mark is awarded for explaining the decrease in butterfly species. 22 GCE Biology B 8BI0 02

23 Question 3 (b) (ii) The majority of candidates gained at least one mark. Most were able to identify that the changes in the moth population matched those in the population of creeping thistle. Surprisingly only about half of candidates suggested a reason, or only gave a vague reason such as "the moths depend on the thistle." Candidates should try to give a specific reason in their explanations, such as a food source, or shelter from predators, rather than using imprecise terms. Examiner Comments This answer gained both marks. The link between moths and thistles is clear and a reason is given for why changes in population of creeping thistle affects the moth population. GCE Biology B 8BI

24 Question 4 (a) (i) Only half of the candidates gained this mark. Many appreciated that blood is pumped to both the heart and lungs in a double circulatory system but the answer needed to imply that the blood is pumped to the heart and lungs separately, as blood is in fact pumped to both the heart and lungs in a single circulatory system. Many (incorrectly) suggested that the system prevented oxygenated and deoxygenated blood mixing, which although true, did not answer the question. A few candidates gave the converse answer and described a single circulatory system without stating why this did not deliver blood at high pressure. Question 4 (b) (i) This question generated a big range in the quality of responses. There were several very detailed explanations of the circulation of tissue fluid that used the information in the graph, along with candidates' own knowledge. There were also, however, many answers that suggested that some candidates were unaware of how tissue fluid is formed. This question also required candidates to compare the two different pressures and credit was not awarded where comparisons were not made. "Tissue fluid is released when the hydrostatic pressure is higher" would gain a mark. "Tissue fluid is released when the hydrostatic pressure is high" would not gain a mark. About half of candidates were able to correctly compare the pressure but far fewer went on to explain that hydrostatic pressure is generated by the contraction of heart muscle and that oncotic pressure is generated by plasma proteins. 24 GCE Biology B 8BI0 02

25 Examiner Comments This answer gained two marks. The candidate makes a correct comparison of the hydrostatic and oncotic pressure and links this to the formation and reabsorption of tissue fluid. They do not explain how the pressures are generated. Examiner Tip Make sure that you make your answer comparative if you are comparing data. Use your own knowledge to explain and analyse data. GCE Biology B 8BI

26 Examiner Comments This answer unfortunately gained no credit. The candidate describes how the hydrostatic and oncotic pressures change along the length of the capillary but does not compare them. 26 GCE Biology B 8BI0 02

27 Question 4 (b) (ii) This question discriminated well between candidates. Many candidates made a good attempt to gain at least one mark. Many were able to recognise that the proteins would build up or accumulate in the tissues and some then went on to explain how this would affect oncotic pressure or water potential. Some candidates did not gain marks due to the use of imprecise language or restating the question stem. Marks were only awarded for a clear implication that the proteins would reduce tissue fluid uptake by the blood (or draw more tissue fluid out of blood). Candidates should be careful not to simply write down the question stem - no credit was awarded for stating that proteins are not removed. Examiner Comments This answer gained both marks. It is clear that the proteins remain, or are stuck, in the tissue fluid and there is an explanation as to how this affects the water potential. Examiner Tip Make sure that you know whether increasing solute concentration will increase or lower water potential. Be careful not to restate the question stem in your answers. GCE Biology B 8BI

28 Question 5 (a) This question was generally well answered. The majority of candidates understand the events that occur during blood clotting and were able to apply their knowledge to the data. Most stated that smoking increased the levels of thrombin and fibrinogen and then explained how this would lead to clot formation. Only a handful recognised that standard deviations were stated in the data and that these indicated that there was no overlap. As a general rule, if standard deviations (or other statistical measures) are included in data, it is good practice to use them when answering the question. This answer only gained one mark. The candidate describes the increase in fibrinogen but not the increase in thrombin. There is no explanation of the roles of thrombin and fibrinogen in clotting. The mark awarded is for the recognition that fibrin production leads to clot formation. Examiner Tip Use standard deviations and carefully select the important data in your answers. 28 GCE Biology B 8BI0 02

29 Examiner Comments This is a high quality answer that gains three marks. There is a clear statement that both thrombin and fibrinogen increase and this is then linked to the clotting cascade. The answer is organised clearly and logically. GCE Biology B 8BI

30 Question 5 (b) (ii) Candidates generally scored highly on this question, with the majority gaining one mark, and many going on to gain a second mark. Most were aware that neutrophils ingest pathogens and many described the digestion of the pathogens. Some candidates confused neutrophils with lymphocytes and described antibody formation. There was evidence that some candidates clearly knew the function of neutrophils but frustratingly used very imprecise language: "eating / taking in" rather than "engulfing", and "destroying / killing" rather than "digesting" are examples of answers that would not gain credit. Examiner Comments This answer clearly gains both marks. There are clear references to engulfing and the digestion of pathogens. Examiner Tip Always use scientific language. Remember that AS is a step up from GCSE and what may have been accepted at GCSE may not be accepted at A level. Examiner Comments This answer would only gain one mark for the idea of phagocytosis. Examiner Tip Always "finish the story" when explaining something. This answer stops half way - the pathogens have been ingested, but what happens next? 30 GCE Biology B 8BI0 02

31 Question 6 (a) This question was found to be difficult by a surprising number of candidates. Many seemed to not be aware that blood and water flow in opposite directions in the gill lamellae of bony fish. A range of different directions were suggested by candidates. Question 6 (c) (ii) Most candidates were able to gain at least one mark, but only a small number went on to gain all three. Unfortunately, some candidates did not refer to the surface area : mass ratio when making the link between the gill surface area with activity levels. There is an important distinction between surface area and surface area : mass ratio. Despite this, many were able to correctly explain that higher activity requires more oxygen, but then did not complete the story by linking this to respiration for muscle contraction. It is important to relate the increased respiration rate to a function rather than simply stating increased respiration. Examiner Comments This answer gained all three marks. There is a clear reference to the surface area : mass ratio increasing with activity which is then linked to oxygen and respiration in the muscles. Examiner Tip State why respiration is needed, for example, respiration linked to muscle activity. GCE Biology B 8BI

32 Examiner Comments This gains two marks. There is a clear reference to surface area: mass ratio and this is linked to oxygen uptake. Respiration is mentioned but it is not put into the context of muscle activity. 32 GCE Biology B 8BI0 02

33 Question 6 (d) Candidates generally scored well on this question and were able to interpret the diagrams to explain why the gill damage would affect oxygen uptake or gas exchange. Most gave relevant descriptions of the effects of the heavy metal ions on the gill structure, usually implying a reduction of surface area, reduction in water flow or reduced contact of gills with the water. Examiner Comments This answer gained both marks. There is a clear explanation of the effect of heavy metal ions in terms of loss of surface area and the candidate then links this with reduced uptake of oxygen. GCE Biology B 8BI

34 Question 7 (a) Most candidates were able to gain at least one mark. "Class" was usually correctly stated along with "Eukarya". There was, however, some confusion as to the genus and species with some candidates picking the wrong species of elephant, inappropriately using capital letters and / or swapping the genus and species names. Candidates should note that genera names begin with a capital letter and species names begin with a lower case letter. Question 7 (b) (i) The majority of candidates gained credit on this question with most making references to the similar appearances of the elephant species. Some gave inappropriate similarities such as large size (which could include other large animals) and some candidates gave a generic definition of different species rather than stating that the elephants had not been observed breeding together. Examiner Comments This answer clearly gains a mark for stating that the elephants are anatomically similar in appearance. Examiner Tip When making a comparison, make sure that you compare appropriate features. Stating that both have a backbone would not be appropriate as many other animals have backbones (but were not thought to be the same species). 34 GCE Biology B 8BI0 02

35 Question 7 (b) (ii) Most candidates were aware of the roles of conferences, peer review and scientific journals in presenting and validating research. A few incorrectly discussed how the DNA data itself could lead to a conclusion rather than explaining how the scientists would agree. Examiner Comments This answer clearly gains a mark by correctly stating that peer review and scientific conferences are used to reach agreement on new evidence. GCE Biology B 8BI

36 Question 7 (d) (iii) This question was found to be difficult by many candidates. There were some excellent, very impressive answers showing that some candidates had looked at the data carefully and used their knowledge of haemoglobin dissociation curves to explain it. Many candidates did not appreciate that if the dissociation curve did not shift in either direction then this would mean that the affinity of haemoglobin for oxygen would not be affected by temperature. There was significant confusion as to whether shifting a curve to the left or right would make it more likely for oxygen to be released or to bind more tightly. Many candidates thought that the affinity of haemoglobin would remain high at cold temperatures enabling the mammoth to obtain oxygen from the air in colder weather. Where candidates appreciated that lowering the temperature increased the affinity of elephant haemoglobin for oxygen (so binding more tightly) they often attained two or three marks. Examiner Comments This answer shows a common mistake - suggesting that when the temperature is lowered, the haemoglobin is still able to bind oxygen which would maintain oxygen uptake. In the case of the elephants used for comparison, lowering the temperature increases the affinity so that in actual fact they would pick up more oxygen from the air. Examiner Tip Make sure that you know what moving the curve to the left and right do to the affinity of haemoglobin for oxygen. 36 GCE Biology B 8BI0 02

37 Examiner Comments This answer gains one mark. There is no reference to oxygen affinity but the candidate does state that oxygen is still released to the tissues. They do not go on to explain why oxygen release to the tissues is beneficial to the mammoth. Examiner Tip Always finish off your answer. Explain why maintaining the release of oxygen to the tissues in the cold is beneficial to the mammoth. GCE Biology B 8BI

38 Question 7 (d) (i)-ii Most candidates were correctly able to read the haemoglobin dissociation curve and identify 10 % for part 7(d)(i). Some candidates did not take sufficient care and used the wrong curve. Part 7(d)(ii) was found to be very challenging for many candidates, with only about one fifth gaining one or both marks. A large number of candidates thought that the answer was simply 10 % of 1.3 cm 3 and did not appreciate how to determine what percentage of oxygen would be unloaded. Some gave incorrect units such as grams. This is an example of a level two maths question that requires candidates to use their maths skills in a biological context. 38 GCE Biology B 8BI0 02

39 Question 8 (b) (i) Many candidates were able to correctly calculate the rate of sucrose transport. A significant number, however, only calculated the mean time and did not use this to then calculate the rate of transport. Question 8 (b) (ii) This question discriminated well between candidates. It required candidates to consider the combined effects of two independent variables on the rate of translocation of sucrose. Encouragingly, most candidates gained some credit and were able to analyse the data to some extent. Many candidates recognised that the inclusion of oxygen increased the rate of transport and also that increasing the temperature in the presence of oxygen increased the rate of transport but did not in the absence of oxygen. Many candidates also made correct references to active processes and the effect of temperature on kinetic energy. Where candidates scored less credit, it was typically due to the use of imprecise language. Many simply stated that increasing the temperature increased the rate when this was in fact only true when oxygen was present. Some candidates correctly described the effects of oxygen and temperature but did not go on to give an explanation as to why this would affect transport of sucrose. Examiner Comments This is a good, well explained answer that describes the effect of oxygen and temperature on the rate of transport and gives an explanation for both. GCE Biology B 8BI

40 Question 9 (a) This question generated a good spread of results with many candidates gaining three or four marks. Candidates are clearly very familiar with the process of allopatric speciation. Most were able to describe the role of geographical separation and a large number specifically used the term allopatric speciation (although there was some confusion with sympatric speciation). There was some confusion over the role of reproductive isolation and candidates need to be careful with the wording of their answers. It needs to be clear that reproductive isolation separates populations within a species and that this will lead to speciation rather than simply stating that different species cannot breed together. More able answers made reference to different selective pressure and the accumulation of genetic differences. Again, care needs to be taken to not suggest that geographical separation causes mutations to occur. 40 GCE Biology B 8BI0 02

41 Examiner Comments This is a very thorough answer that correctly describes the geographical separation, reproductive isolation, allopatric speciation, different selective pressures and a change in allele frequencies. The candidate does incorrectly mention sympatric speciation but has already gained maximum marks. Examiner Tip Be careful with the wording of your answers. Reproductive isolation in this context should be something that helps to cause speciation and not a consequence. GCE Biology B 8BI

42 Question 9 (b) The majority of candidates gained at least one mark although there was some confusion as to whether there would be an increase or decrease of genetic disorders in the tiger populations. More able answers described a fall in frequency of genetic disorders and explained this by referring to tigers from different populations breeding together or having wider gene pools. Some candidates thought that the tiger populations would breed with each other and this would cause harmful alleles to spread and increase the frequency of disorders. Candidates should be careful when using the terms inbreeding and interbreeding - they mean very different things. Examiner Comments This answer gains both marks. The candidate correctly states that the frequency of disorders will fall and that this is linked to a larger gene pool. Examiner Tip Use technical vocabulary such as "gene pool" where appropriate but be careful to use the correct terms. Inbreeding and interbreeding are often confused and do not mean the same thing. 42 GCE Biology B 8BI0 02

43 Paper Summary Based on their performance in this examination, candidates are offered the following advice: be prepared to analyse unfamiliar data. Gain as much practice as possible use scientific knowledge and understanding when giving explanations use accurate, scientific vocabulary in answers plan answers carefully so that they are precise and not over verbose be familiar with all the necessary maths skills that are listed in the specification be familiar with the core practicals and have full understanding of how to plan and criticise experiments. GCE Biology B 8BI

44 Grade Boundaries Grade boundaries for this, and all other papers, can be found on the website on this link: 44 GCE Biology B 8BI0 02

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